Seismic data acquisition and processing techniques are used to generate a profile (image) of a geophysical structure (subsurface) of the strata underlying the land surface or seafloor. Among other things, seismic data acquisition involves the generation of acoustic waves, the collection of reflected/refracted versions of those acoustic waves, and processing the collected seismic data to generate the image. This image does not necessarily provide an accurate location for oil and gas reservoirs, but it may suggest, to those trained in the field, the presence or absence of oil and/or gas reservoirs. Thus, providing an improved image of the subsurface in a shorter period of time is an ongoing process in the field of seismic surveying.
In the age of large channel count seismic crews it is becoming increasingly difficult to realize high productivity while constrained by current field deployment techniques. In addition to improving productivity, there is also an almost constant search to improve sensor coupling and reduce spread noise. The issue is that simple forms of productivity improvement do not necessarily translate into better data quality.
Reduction of human interaction associated with field deployment techniques can be achieved through the reduction of the electrical connections between sensors and the acquisition system, for example, through the use of short cable segments and integrated connectors that have an arrangement which keeps the sand out. The resulting reduction in electrical connections significantly simplifies the sensor deployment method, facilitating mechanized deployment.
Early ideas of mechanized or automated deployment centered on affixing sensors to an acquisition cable. Each sensor would have a short cable segment, referred to as a stringer that would mate to a digitizing module or digitizing unit (DU) on the acquisition cable. Initially, significant time is spent attaching the sensors to the acquisition cable through this arrangement of stringers and DUs. Once attached, the sensors remain connected at all times. The resulting arrangement requires the entire assembly to be wrapped onto a large spool for deployment or wound into a bin, for example in a figure-eight arrangement.
Given the directionality of the sensors, planting the sensors so that all sensors end up planted with some consistency is difficult to manage. The acquisition cable inevitably twists during the spooling efforts, and the layout crew spends a significant amount of time righting the sensors. In addition to the time concerns, the resulting spools or bins of equipment are bulky and difficult to manage as the individual sensors are heavy. Efficient trouble shooting and field repairs are difficult given that replacing even a single sensor requires removing and re-applying all of the tape and zip ties. One alternative to this arrangement is a gimbaled sensor; however, gimbaled sensors are not known for reliability.
Electrically disconnecting the sensor from the acquisition system has its own challenges to consider. For example, in order to maintain fidelity the analog sensor data need to be digitized and transferred to the recording unit. Therefore, structures are desired that provide a wireless communication link between a sensor and a DU. These structures would provide the required power to the sensor and DU through either a continuous power source or a battery. Conventional batteries, however, are costly, voluminous and require recharging. Therefore, improved rechargeable batteries and an adequate method for recharging the batteries are also desired.